Sturge-Weber syndrome (SWS), also known as encephalofacial angiomatosis, is a neurocutaneous disorder that occurs as a sporadic, congenital condition characterized by a port-wine stain (PWS) affecting the V1 territory of the face (the forehead and/or eyelid) associated with a leptomengial angioma of the brain and venous abnormalities of the eye. It occurs in both males and females, in approximately 1 in 20-50,000 live births. Independently occurring port-wine stains are much more common, occurring in approximately 3 in 1000 births and commonly involve the head and neck. A child born with a port-wine stain on the face has approximately a 6% chance of having SWS, and this risk increases to 26% when the PWS is located in the V1 territory of the face. Port-wine stains commonly have underlying soft and bony tissue hypertrophy which may be mild or massive. When a port-wine stain-associated hypertrophy involves a limb and has enlarged venous or lymphatic vessels this is referred to as Klippel-Trenaunay Weber syndrome (KTWS). KTWS has been reported in association with SWS when the PWS is extensive and extends down on to the trunk and affected limb. Therefore, it has been hypothesized that SWS, KTWS, and PWS are likely to have the same underlying somatic mutation(s). According to this hypothesis the precise clinical manifestations are dependent upon where and when in the developing fetus the somatic mutation occurs.